In order to satisfy determined requirements, it is sometimes necessary to lower and/or raise a rotorcraft having contact members resting on the ground, with these operations sometimes being referred to as “kneeling” and “erecting”.
Lowering makes it possible in particular to load a helicopter in a small space such as the hold of a ship, or indeed a hangar of small dimensions.
Furthermore, in naval use, lowering increases the stability of a helicopter while it is standing on the deck of a ship, since lowering the helicopter lowers its center of gravity. In addition, when the ground clearance is small, where ground clearance is the height between the ground and the fuselage, it is easier to tie down the helicopter.
In contrast, raising the helicopter is an operation that can be useful, for example, in order to allow a vehicle to pass under the tail boom of the rotorcraft so as to penetrate into its hold.
In order to lower or raise an aircraft, devices are known that act on the undercarriages thereof, causing them to pass from a normal position to a low position or to a high position.
More precisely, document FR 2 608 242 discloses a damper-actuator that performs a function of damping an undercarriage and a function of retracting it, while also enabling it to be shortened or lengthened.
That damper-actuator is fitted to a rocker-beam undercarriage of a rotorcraft. Conventionally, it serves to extend or retract the undercarriage into a well provided for this purpose, while also performing a shock-absorbing function.
That damper-actuator includes a rod in which a first sliding piston defines an outlet chamber, which itself slides in a body by means of a second piston defining a retraction chamber. Thus, that device makes operations of lowering or raising possible by causing the undercarriage to go from a normal position to a lowered position or a raised position.
In order to lower a rotorcraft, an operator causes the outlet chamber to communicate with a hydraulic circuit while the pressure in the retraction chamber is low. The weight of the rotorcraft then causes the rod to penetrate into said body, so as to pass from a normal position to a lowered position. The rotorcraft is then in a lowered position.
In order to return to the normal position, it is necessary to put pressure back into the outlet chamber with the help of the hydraulic circuit. Similarly, in order to raise the rotorcraft, said pressure is raised even further so as to cause the rod to pass from a normal position to a raised position.
Consequently, such a device provided with at least one undercarriage including a damper-actuator can perform raising and lowering operations. Nevertheless, it is found that the device makes only three positions available, i.e. a lowered position, a normal position, and a raised position. Furthermore, each change requires action on the part of an operator.
In addition, ground clearance depends not only on the position adjustment, but also on the load of the aircraft, insofar as the damper-actuators of the undercarriages shorten to a greater or lesser extent depending on the total weight of the aircraft. If this weight is wrongly estimated that can lead to incidents insofar as the required ground clearance is not reached, e.g. because the wheels have been flattened excessively.
If the tires on the wheels are not inflated sufficiently, then ground clearance will be lower than expected, which can cause the equipment disposed under the fuselage of the aircraft, e.g. a radome, to be destroyed.
Similarly, outside temperature can have an influence on ground clearance.